1. Field of the Invention
The present invention relates to a liquid ejection head, a liquid ejection apparatus and a method of manufacturing a liquid ejection head, and more particularly, to a structure for improving the durability of the liquid ejection head and a method of manufacturing the liquid ejection head having the above-described structure.
2. Description of the Related Art
In general, an inkjet recording apparatus which forms a desired image by ejecting ink droplets from a liquid ejection head onto a recording medium has been widely used as a generic image forming apparatus. In inkjet recording apparatuses, various innovations have been applied to the structure and shape of the flow channels inside the liquid ejection head in order to achieve high-speed ejection by improving the ejection efficiency and improving the refilling efficiency.
Japanese Patent Application Publication No. 2002-113871, Japanese Patent Application Publication No. 11-048483 and Japanese Patent Application Publication No. 2004-155203 describe a liquid ejection head of a thermal type, having a structure which comprises a movable member that faces a heating body at a spacing interval from the heating body. The movable member of the liquid ejection head described in Japanese Patent Application Publication No. 2002-113871, Japanese Patent Application Publication No. 11-048483 and Japanese Patent Application Publication No. 2004-155203 is formed in a cantilever structure, one end thereof being fixed to a step section provided to the upstream side of the ink chamber (the side of the common liquid chamber), and the other end thereof, which is on the downstream side of the ink chamber (the side of the ejection port) being formed as a free end. When an air bubble is created in the vicinity of the heating body by a film boiling effect, the free end of the movable member which is provided at a position opposing the heating body deforms so as to open widely toward the ejection port side, and hence the direction of propagation of the pressure produced by the creation of the bubble is guided toward the downstream direction, and the pressure of the bubble contributes directly and efficiently to ejection. Furthermore, the actual growth of the air bubble is guided toward the downstream direction, similarly to the direction of propagation of the pressure, and the bubble grows larger in the downstream side of the movable member than in the upstream side of the movable member. In other words, the liquid ejection head described in Japanese Patent Application Publication No. 2002-113871, Japanese Patent Application Publication No. 11-048483 and Japanese Patent Application Publication No. 2004-155203 is able to improve the fundamental ejection characteristics, such as the ejection efficiency, the ejection force, the ejection speed, and the like, by controlling the actual growth direction of the bubble and controlling the propagation of the pressure of the bubble by means of the deformation of the movable member.
However, the movable member provided in the liquid ejection head described in Japanese Patent Application Publication No. 2002-113871, Japanese Patent Application Publication No. 11-048483 and Japanese Patent Application Publication No. 2004-155203 is displaced by several micrometers to several ten micrometers every time a bubble is created by the heater, and therefore a large stress is generated repeatedly in the movable member and problems such as deformation or breaking of the movable member occur.
In the liquid ejection head described in Japanese Patent Application Publication No. 2002-113871, right-angled sections, acute-angled sections, burrs, and the like formed at the edges of the movable member, are removed, thereby alleviating the concentration of stress, and hence the occurrence of cracks in the movable member or breaking of the movable member is prevented to some extent. However, small cracks do occur in the movable member due to the repeated deformation, and no countermeasures are provided for preventing breakage of the movable member due to these small cracks.
Japanese Patent Application Publication No. 11-048483 discloses technology for covering a movable member with a coating, from the viewpoint of improving resistance to corrosion by the liquid and preventing electrical corrosion. However, countermeasures are not proposed for preventing the deformation of the movable member or the breaking of the movable member as a result of the repeated stress applied to the movable member during the ejection of liquid.
In the liquid ejection head described in Japanese Patent Application Publication No. 2004-155203, a movable member is constituted by laminated layers of metals having different stresses (tensile stress and compressive stress), with the aim of achieving highly accurate positioning of the movable member, controlling the thickness of the movable member and reducing the deformation energy created by forming the member so as to adopt a warped state. On the other hand, Japanese Patent Application Publication No. 2004-155203 does not mention the fact that a repeated stress is applied to the movable member by the ejection of liquid, and the liquid ejection head described in Japanese Patent Application Publication No. 2004-155203 does not propose countermeasures against the deformation of the movable member or the breaking of the movable member as a result of this stress.